1. Field of the Invention
This invention relates to a method of fabricating a complementary metal-oxide-semiconductor (CMOS) sensor device, and more particularly, to a method of fabricating microlens on a color filter.
2. Description of Related Art
Conventionally, for a PC camera and a digital camera, CMOS sensors are frequently used. A typical CMOS sensor diode includes a sensor layer on the substrate. The sensor layer has different sensor areas to detect different color light. On the sensor layer, there is a passivation and there is a color filer on the passivation. Furthermore, a color filter is formed on the passivation. The incident light usual has different color and incident angles. As the incident light penetrates through the color filter, it is divided into three color light, such as red light, green light or blue light and then absorbed and sensed by the corresponding sensor area.
FIG. 1A to FIG. 1F illustrates the process flow of fabricating a conventional CMOS sensor device. First, referring to FIG. 1A, on a substrate 100, a passivation layer 102 is formed. A color filter 108, including red filter 108a, green filter 108b and blue filter 108c, is formed on the passivation layer 102. The color filter 108 is made from acrylic material. Next, a planarized layer 103 is formed over the passivation layer 102 and the color filter 108. An opening 104 and an opening 106 are defined on the planarized layer 103 and the passivation layer 102. The opening 104 is for connecting the pad and the opening 106 is for connecting the scribe. Then, a microlens resist layer 110id formed over the opening 104, the opening 106 and the planarized layer 103. It is observable that the microlens resist layer 110 has different thickness at different points.
Especially, the photoresist in the opening 104 has a thickness Hi of about 4-5 .mu.m.
Next, referring to FIG. 1B, a photoresist layer 112 is formed and patterned on the microlens resist layer 110. Then, referring to FIG. 1C, as the photoresist layer 112 as a mask, the microlens resist layer 110 is etched to expose the opening 104 and the opening 106. Then, referring to FIG. 1D, the photoresist layer 112 is removed to expose the patterned microlens resist block 110a. The microlens resist block 110a is aligned to the color filter 108. The microlens resist block 110a includes a number of protuberances 110a. The cross section of each protuberance 110a can be rectangle or polygon.
Next, referring to FIG. 1E and FIG. 1F, an after-development-exposure step is performed so that the microlens resist blocks 110a becomes a number of semi-circle microlens 110b. Then, after curing treatment onto the semi-circle microlens 110b, conventional microlens structure of a color filter of a CMOS sensor device is accomplished.
However, the conventional process for forming CMOS sensor device has lots of drawbacks. For example, the thickness of the microlens resist layer 110 in the pad opening 104 is more than at other point for about 4-5 .mu.m. As a result, the exposure energy required for different points has a great variety. If an exposure energy suitable for exposing the region around the color filter 108 is used, scum effect will occur in the pad opening due to insufficient energy. On the other hand, if an exposure energy suitable for exposing the region around the pad opening 104 is used, after exposure and development, the defined microlens resist block 110a will have shrinking size, even, of 2-3 .mu.m. That is because of over-exposure. Especially for pixel size of less than 10 .mu.m, error of 2-3 .mu.m produces a great influence.